1. Field of the Invention
The present invention relates to a color wheel suitable as a filter element of a time-share dispersing device, and to a manufacturing method thereof.
2. Description of the Related Art
Color composition in a projection-type image display apparatus has conventionally been accomplished commonly by a method, such as: a single-panel method, in which one light valve element adapted to control light amount per pixel thereby creating an image is used to disperse each pixel into R (red), G (green), and B (blue) lights; or a three-panel method, in which three light valve elements dedicated respectively to R, G and B lights are used to produce R, G and B images in parallel, and then the three images thus produced are composed. Recently, as a light valve element capable of fast switching, such as a ferroelectric liquid crystal display element or a digital micro-mirror device, is increasingly coming into practical use, a time-sharing single-panel method is widely used. In the time-sharing single-panel method, R, G and B lights are caused to sequentially impinge on one light valve element, the light valve element is driven in synchronization with switching-over of the R, G and B lights thereby producing R, G and B images in a time-series manner, and the images thus produced are projected onto a screen, or the like. Here, color composition of the images is accomplished by a viewer due to an afterimage effect occurring at a sense of vision. In the time-sharing single-panel method, reduction in both dimension and weight of the apparatus, which is a feature of a single-panel method, can be achieved by employing a relatively simple optical system, and therefore the time-sharing single-panel method is favorable for realizing inexpensive fabrication of a projection-type image display apparatus. In such an image display apparatus, a color wheel is preferably used as a filter element of a time-share light dispersing device to sequentially disperse light emitted from a white light source into R, G and B lights having respective wavelength bands in a time-sharing manner.
FIGS. 4A and 4B are respectively top plan and side views of a conventional and typical color wheel assembly 200 as a time-share light dispersing device incorporating such a color wheel. Referring to FIG. 4B, the color wheel assembly 200 includes a color wheel 100, and a driving motor 106 provided with a motor hub 105. The color wheel 100 is a tricolor color wheel composed of a disk-like substrate 101 which is made of a light-transmitting material, for example, optical glass, and three pie-shaped (sectorial) filters 102, 103 and 104 which are formed on a surface of the substrate 101, and which transmit exclusively, for example, R, G and B lights, respectively. The color wheel 100 thus structured is fixedly attached to the motor hub 105 coaxially therewith. The color wheel assembly 200 operates such that the color wheel 100 is spun by the driving motor 106 so that white light S impinges sequentially on the filters (R, G and B) 102, 103 and 104 whereby the white light S is sequentially dispersed into R, G and B lights.
There are two types of color wheel structures: a monolithic type structured such that respective color filters are formed on a single disk-like substrate; and a segment type structured such that respective color filter segments separately prepared in a pie shape are fixedly attached to one another so as to form a color filter disk.
FIGS. 5 and 6 show respectively top plan and exploded side sectional views of a segment type color wheel 160 including a plurality (four in FIG. 5) of sectorial color filter segments 112, 114, 116 and 118 which are separately prepared and are fixed in position by means of a support member 120 and a clamp member 122 so as to form a color filter disk.
Specifically, as shown in FIG. 6, respective inner circumferences 112a, 114a, 116a and 118a of the color filter segments 112, 114, 116 and 118 are fitted to the outer circumference of a smaller cylinder portion 120a of the support member 120 whereby the color filter segments 112, 114, 116 and 118 are duly set in position with respect to the radial direction of the color wheel 160, and surfaces thereof toward the inner circumferences 112a, 114a, 116a and 118a are fitted to an annular seat portion 120b of the support member 120 whereby the color filter segments 112, 114, 116 and 118 are duly set in position with respect to the thickness direction of the color wheel 160. Then, a smaller cylinder portion 122a of the clamp member 122 is engagingly inserted into a hollow 120c of the support member 120 so that an annular seat portion 122b of the clamp member 122 and the aforementioned annular seat portion 120b of the support member 120 sandwich and clamp the inner circumferential portions of the color filter segments 112, 114, 116 and 118. And, when the support member 120 and the clamp member 122 are bonded or screwed together, the color filter segments 112, 114, 116 and 118 are securely fixed in position. The color wheel 160 thus structured is fixedly attached to a hub (such as the hub 105 as shown in FIGS. 4A and 4B) of a motor (such as the driving motor 106 as shown FIG. 4B) such that the hub is inserted in the hollow 122c of the clamp member 122 constituting the color wheel 160 (refer to, for example, Japanese Patent Applications Laid-Open Nos. 2004-101827 ([0010], and FIG. 4) and H10-48542 (claim 1, and FIG. 2).
The segment-type color wheel 160 shown in FIGS. 5 and 6 employs the support member 120 to precisely position and fix the color filter segments 112, 114, 116 and 118, but in some segment-type color wheels, color filter segments are directly fitted to a motor hub of a driving motor (for example, the motor hub 105 of the driving motor 106 as shown in FIGS. 4A and 4B). In any cases of segment-type color wheels, a rotary member having a circumferential surface, such as the support member 120 or the motor hub 105, is fixedly set at the center of the color filter disk constituted by the color filter segments 112, 114, 116 and 118, whereby a color wheel can be rotated at a high speed. On the other hand, a monolithic-type color wheel has an integral structure and does not require a support member, but still a rotary member having a circumferential surface, such as the motor hub 105 of the driving motor 106, has to be attached to the monolithic-type color wheel.
In both a monolithic-type color wheel and a segment-type color wheel, a rotary member with a circumferential surface (hereinafter refereed to simply as “a rotary member”) is fixed to a color filter disk usually by using adhesive alone or in combination with other fixing methods. If the adhesive applied for fixing the rotary member to the color filter disk is not cured completely, then it can happen that when the color filter disk is rotated at a high speed, for example, at the inspection process, uncured portions of the adhesive are scattered out on the surface of the color filter disk in the radial direction and turn into scattered adhesives 170 as shown in FIG. 7. The scattered adhesives 170, even if minute, have negative effects on the optical characteristics of a light transmitting area, thus lowering the production yield rate of color wheels.
The problem of adhesive scattering is caused by inadequate curing which results from unevenness of adhesive layer thickness or non-uniformity of adhesive application range, or which is attributable to adhesive chambers existing at the joint surfaces of the color filter disk and the rotary member. Also, when the adhesive is UV-curable, the problem of adhesive scattering can happen not only due to an excessive adhesive layer thickness but also to a too scarce adhesive layer thickness which does not allow an ultraviolet ray to duly penetrate through the adhesive layer.